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New Scientist Live

Giraffes spend their evenings humming to each other

Martin Harvey/Alamy Stock Photo

By Karl Gruber

We are familiar with many animal sounds – a lion’s roar, a dog’s bark, a parrot’s squawk – but what sound comes to mind when you think of a giraffe? The long-necked beasts make basic sounds like snorts or bursts through their nose, but nothing you could identify with a nice label – until now.

Biologists say they have discovered that giraffes hum. People had earlier speculated that giraffes are unable to produce any substantial sounds because it is physically difficult for them to generate sufficient airflow through their long necks to produce vocalisations. Others have suggested giraffes use low frequency “infrasonic” sounds – sounds below the level of human perception – much like elephants and other large animals do for long-range communication.

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After reviewing almost 1000 hours of sound recordings in three European zoos, Angela Stöger at the University of Vienna, Austria, found no evidence of infrasonic communication – but she did pick up a weird humming coming from the giraffe enclosures in all three zoos at night.

“I was fascinated, because these signals have a very interesting sound and have a complex acoustic structure,” she says.

The “hum” turned out to be a low frequency sound, of about 92 hertz. That’s not infrasound – we can still just about hear it unaided. Stöger and her colleagues say the hum varies in duration and contains a rich combination of notes.

Listen to giraffe humming here:

Giraffes have a socially structured system, and for a long time scientists have been trying to figure out how they communicate, says Meredith Bashaw at the Franklin & Marshall College in Lancaster, Pennsylvania. “This new vocalisation could add a piece to that puzzle,” she says.

Why the humming?

Bashaw says she can imagine a few potential roles for this humming. “It could be passively produced – like snoring – or produced during a dream-like state – like humans talking or dogs barking in their sleep,” she says. Alternatively, it could be a way for giraffes to communicate with each other in the dark, when vision is limited, to say, “hey, I’m here”, she adds.

Unfortunately, Stöger says, she and her colleagues were not able to observe the giraffes mid-hum, so we don’t know about the behaviours associated with the sounds. But vocalisations in other species with similar social structure is known to convey information about things like age, gender, sexual arousal, dominance or reproductive states, she says.

John Doherty, at Queen’s University Belfast, studies giraffes in Samburu Reserve in northern Kenya. “I have once come across audible vocalisation reminiscent of [the] recordings, again in a captive giraffe,” he says. “But, in this case, [the giraffe] was clearly disturbed by a husbandry procedure being carried out on its calf in a separate but visible enclosure.”

“It could be passively produced – like snoring – or produced during a dream-like state ”

“I am very tired. The noise is still there,” one resident told the Torquay Herald Express. “I am being disturbed in the night and am being kept awake by this.”

However, despite the new findings, Paignton Zoo officials deny any giraffe involvement. “No, definitely not linked to our neighbour’s issue – but the image of our giraffes humming happily to themselves all night is a delightful one!” says Phil Knowling, press and public relations officer at Paignton Zoo.

Stöger agrees that it is unlikely that the humming would have caused a disturbance. “The giraffe signals are not so intensive. I personally doubt that neighbours would hear that,” she says.